1. Field of the Invention
The present invention relates to a centering device which is used with a lathe and which is particularly suitable to center a long work to be threaded.
2. Description of the Prior Art
Referring to FIG. 19, there is shown a conventional centering device including a plurality of work rests R (only one is shown in FIG. 19) mounted on a bed B and spaced from each other by a predetermined distance for supporting a long round bar or a work W to be threaded. Each of the work rests R is constructed as a manually operable jack and is adjustable in its height so as to center the work W which is clamped by a traveling stay (not shown) mounted on a carriage (not shown).
However, such a thread cutting operation requires several, ten times (for example, twenty times for a P-6 thread) of reciprocal movements of the carriage, so that the operation for moving the position of the work rests R or the operation for mounting and removing the same must be frequently performed. Therefore, the conventional centering device involves the problem that the operation is very troublesome. Further, although the feeding speed of the carriage has now been increased by use of a cutting tool made of cemented carbide in place of one made of high speed tool steel, the thread cutting operation cannot be efficiently performed because of the above troublesome operation.